#include <iostream>
#include <unordered_map>

using namespace std;
int n; string s; 
unordered_map<char, int> mp;

bool check()
{
    for(int i = 0; i < n; i++)
    {
        char ch1 = s[i];
        char ch2;
        if(isupper(ch1))  ch2 = tolower(ch1);
        else ch2 = toupper(ch1);
        if(!mp.count(ch2)) return 0;
    }
    return 1;
}

int main()
{
    cin >> n >> s;
    for(int i = 0; i < n; i++) mp[s[i]]++;
    if(check()) cout << "YES" << endl;
    else cout << "NO" << endl;
    return 0;
}